With rapid development of digital technology, at present many industries and individuals commonly use electronic documents to process data and store information, and contents in the electronic documents are generally displayed on paper by means of printing, copying, and the like, for reading and dissemination. However, for enterprises and institutions, political parties and government agencies, and departments relating to state security and the like usually involving a large amount of confidential information (such as contract, secret, and similar important documents), a lot of important information or confidential information is very likely to be leaked out through these paper documents. Therefore, it is necessary to take some security measures to prevent leaking of document information caused by paper documents generated through printing, copying, and similar operations. However, with gradual increase in volume of business of each unit, continuous expansion of unit size, and increase of staff number, costs and difficulties of various management increase accordingly, and it is difficult for administrator or leader to timely control document printing situations within the unit, bringing big challenges to security measures to some extent, and increasing possibility of leaking of important document information. Further, for printed paper documents and their copies, generally source of document printing cannot be identified and printing content cannot be audited due to lack of document source tracking information, leading to ad libitum printing of paper documents and intentional or unintentional illegal dissemination, and further increasing difficulties in document printing management and control. Therefore, researches on printing process management and control of electronic documents, document source tracking, and content auditing are important and challenging topics.
At present, printer can be basically divided into four types: local printer, shared printer, network printer and virtual printer. For ordinary enterprises and institutions, shared printer, network printer and virtual printer are generally used for printing, while for enterprises and institutions with high confidentiality requirements, such as security offices (for example army), in consideration of business requirements or safety, means like network printing are seldomly used, and in more situations local printer is used for printing, that is, each client computer is directly connected to a physical printer for printout, and respectively manages its own printed documents, avoiding the problem of information leakage therebetween.
At present, printing monitoring and auditing technology implements printing management and control mainly through deploying printing management and control service program to client. When user initiates printing operation, printing management and control service program deployed to the client can obtain print job information and printing document data stream by monitoring print port or the like, and then save the printing record information in a database server, or save the printing document data stream on a file server. The printing service program on the server performs related processing after obtaining a related printing request, for example, saving the printing information record and the original printing content, then performs printout according to the user's request, thus completes the entire document printing control process. This method achieves the purpose of centralized management and control of document printing to some extent, but the following problems exist: first, configuration information on the client is not flexible enough, management and control means is relatively simple, specifically, only control of print permission to a printer can be achieved, for example, whether a client can use the printer can be controlled, while for different types of printers, different types of application programs, and different models of printers, personalized setting cannot be performed, and printing control strategy also cannot be dynamically updated in real time, but is achieved only by means of registration and the like; second, for printed paper documents and their copies, effective means of source tracking cannot be provided, and therefore the purpose of actual print job auditing cannot be achieved, and defects in closed-loop management of paper documents exist. More details on these types of printer monitoring and auditing technology researches can be found in the article “Techniques research of printing monitor and audit” published in  Computer Engineering and Design, No. 2, 2009.
Furthermore, at present some other methods of implementing printing management and control operation have also been proposed. For example, in Chinese patent application “Document printing management and control system and method” with application No. 200610156904.9, a method for monitoring printing of confidential document is proposed. This method involves document format conversion, and requires backing up the original data of the confidential document at different levels in advance for comparison and checking, thus has poor flexibility. In another example, in Chinese patent application “Multi-point document printing control system and method” with application No. 200510032985.7, a printing management and control method by means of virtual printing is proposed. This method can monitor multiple printers through resource safety control center checking whether a print job is illegal according to printing strategy saved thereon. The disadvantage of this method is that judgment rules for all printers are unified, and cannot have personalized setting for different clients. At the same time, all these methods lack means of document source tracking and contents auditing.